The present invention disclosed herein relates to image sensors. More particularly, the present invention disclosed herein relates to an image sensor having a temperature sensor and a driving method thereof.
With the ever-growing evolution of digital technology, digital cameras are typical apparatuses in a variety of digital electronic products. Essential elements governing a quality of the digital camera are an optical lens and an image sensor. The image sensor operates to generate an electrical signal from light incident on the optical lens, representing a picture of good quality.
An image sensor generally has a pixel array, i.e., pluralities of pixels arranged in a matrix of two dimensions. Each pixel includes photosensitive means, and transmission and readout devices. According to types of the transmission and readout devices, the image sensors are generally classified into two kinds such as charge-coupled devices (CCD) and complementary metal-oxide-semiconductor image sensors (CIS). The CCD uses MOS capacitors for transferring and outputting signals, in which the MOS capacitors are adjacent to each other and charge carriers are stored in the MOS capacitor and conveyed to the adjacent capacitor by potential gaps. Different from that, the CIS operates in a switching mode by which MOS transistors detect outputs in sequence by the number of pixels.
The CCD is better than the CIS in noise and image quality, but has disadvantageous in product cost and power consumption over the CIS. In other words, the CIS has advantages of lower power, singularity of voltage and current source, small power consumption, compatibility to consolidate CMOS circuits, random access to image data, cost reduction by using standard CMOS technology, and so on. Accordingly, applications of the CIS are now expanding across digital cameras, smart phones, personal digital assistants (PDA), notebook computers, security cameras, barcode readers, high-definition televisions, resolution cameras, electronic playthings, and so forth.
Those image sensors are still required to increase distinction and reduce noise for the purpose of functioning like human eyes. Although image signal processors (ISP) have been recently added to improve the characteristic of noise susceptibility, they are still insufficient for confronting an increase of thermal noises inherent in the sensors itself.